This invention relates to a process for the catalytic hydrogenation of maleic anhydride in the liquid phase to produce gamma-butyrolactone.
The continuous hydrogenation of dicarboxylic acids and dicarboxylic anhydrides, including maleic anhyride, has been disclosed in German Offenlegungsschrift 1,901,870 where hydrogenation of the anhydride is conducted under pressure in the liquid phase at a temperature of about 180.degree. to 280.degree. C. The process is, however, primarily directed to the formation of tetrahydrofuran. If one wishes to obtain gamma-butyrolactone, the process requires higher hydrogen pressures and the butyrolactone must be quickly separated from the reaction mixture. This process has an additional disadvantage in that considerable amounts of polymeric products are formed. German Auslegeschrift 1,668,348 discloses a process for producing gamma-butyrolactone from maleic anhydride by hydrogenating in two stages with different catalysts. Hydrogenation in the gaseous phase is disclosed under a pressure ranging from 0.1 to 5 kg/cm.sup.2 and at temperatures of 180.degree. to 290.degree. C. in the first stage and of 220.degree. to 330.degree. C. in the second stage. As it is operated in the gaseous phase, conversion rate and performance are relatively low in this process.
It is an object of the present invention to provide a continuous process for producing gamma-butyrolactone by hydrogenating maleic anhydride in the liquid phase to provide high yields of gamma-butyrolactone having a high degree of purity.
Other objects and advantages will become apparent from a reading of the following detailed description and examples.